Wednesday, 20 June 2012

cset shield - easily configure cpusets


Basic concept - 3 cpusets
root: present in all configurations and contains all cpus (unshielded)
system: contains cpus used for system tasks - the ones which need to run but aren't "important" (unshielded)
user: contains cpus used for "important" tasks - the ones we want to run in "realtime" mode (shielded)

The shield command manages these 3 cpusets.

During setup it moves all movable tasks into the unshielded cpuset (system) and during teardown it moves all movable tasks into the root cpuset.
After setup, the subcommand lets you move tasks into the shield (user) cpuset, and additionally, to move special tasks (kernel threads) from root to system.

Create a shield (Example: 4-core non-NUMA machine: we want to dedicate 3 cores to the shield, and leave 1 core for unimportant tasks; since it is non-NUMA we don't need to specify any memory node parameters; we leave the kernel threads running in the root cpuset)

    $ cset shield --cpu 1-3

Some kernel threads (those which aren't bound to specific cpus) can be moved into the system cpuset. (In general it is not a good idea to move kernel threads which have been bound to a specific cpu)

    $ cset shield --kthread on

List what's running in the shield (user) or unshield (system) (-v for verbose, list the process names) (2nd -v to display more than 80 characters)

    $ cset shield --shield -v
    $ cset shield --unshield -v -v

Stop the shield (teardown)

    $ cset shield --reset

Execute a process in the shield (commands following '--' are passed to the command to be executed, not to cset)

    $ cset shield --exec mycommand -- -arg1 -arg2

Move a running process into the shield (move multiple processes by passing a comma separated list, or ranges (any process in the range will be moved, even if there are gaps))

    $ cset shield --shield --pid 1234
    $ cset shield --shield --pid 1234,1236
    $ cset shield --shield --pid 1234,1237,1238-1240

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